The authors used a liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for measuring 25(OH)D – the storage form of vitamin D in the body – in the US population across two time periods: 1988–2006 and 2007–2010.
According to results published in the American Journal of Clinical Nutrition, 25(OH)D levels were stable from 1988 to 2006, but an increase was observed from 2007-2010.
“Of particular interest is the significant increase in 25(OH)D in the population after 2006. It is difficult to know exactly when the interest in the potential healthful effects of vitamin D filtered down to the average American, but the increase in 25(OH)D in NHANES 2007–2010 appears to be consistent with several temporal trends,” wrote the authors. “Toward the end of the decade, surges in 25(OH) D testing and vitamin D deficiency diagnoses were reported, health care providers increasingly recommended vitamin D supplements at doses higher than the 1997 Dietary Reference Intake recommendations, and a growing number of foods were fortified with vitamin D.
“Consumer spending on vitamin D supplements increased by [more than] 10-fold between 2001 and 2009. Together, these data support the upward shift in the vitamin D status of the population at the end of the past decade, particularly in those taking vitamin D supplements.”
“A valuable contribution to the growing body of evidence”
Commenting on the study’s findings, Andrea Wong, PhD, VP of Scientific & Regulatory Affairs at the Council for Responsible Nutrition (CRN), told us: “The scientific evidence of how vitamin D impacts human health has expanded exponentially over the past decade. Hundreds of new studies on vitamin D have reinforced its role in bone health and have identified a myriad of other health benefits. Vitamin D continues to be a dynamic area of research that carries significant public health implications, which is why it is so important to have accurate tools to measure vitamin D status. Confident measurements of vitamin D status can help inform future nutrition policies and this study is a valuable contribution to the growing body of evidence on vitamin D.
“This study also demonstrates the progress that has been made to improve the accuracy and consistency of vitamin D measurements to help bridge the gap between clinical studies and public policy. While the study results show that vitamin D status has increased modestly in recent years, many Americans continue to fall short of this important nutrient.”
Vitamin D Facts
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. Both D3 and D2 precursors are transformed in the liver and kidneys into 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D).
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Led by Rosemary Schleicher from the US Centers for Disease Control and Prevention (CDC), the researchers used data from the cross-sectional NHANES from 1988 through 2010.
Because of non-standardized serum 25(OH)D measurements, temporal trends in the vitamin D status have been difficult to assess, so the researchers used a liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for measuring 25(OH)D from 38,700 people in the 1988–2006 surveys and 12,446 people in the 2007–2010 surveys.
Results showed that vitamin D levels remained stable for 1988 to 2006, but there was a 5-6 mmol/L increase for 2007-2010.
A significant percentage of non-Hispanic blacks (46-60%) and Mexican Americans (21-28%) had levels of 25(OH)D lower than 40 nmol/L compared to non-Hispanic whites (6-10%), said the researchers.
“When we looked at supplement usage with the use of the NHANES data, we saw that, overall, the use of vitamin D–containing supplements has been stable for several decades,” they wrote. “However, more persons in selected groups, in particular those persons [greater than] 40 y old, females, and non-Hispanic whites, used higher-dose supplements in 2007–2010.
“In addition to clarifying secular trends in vitamin D status of the US population, the present study highlights the importance of standardizing 25(OH)D measurements by using assay methods that are traceable to international reference materials.”
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.115.127985
“The vitamin D status of the US population from 1988 to 2010 using standardized serum concentrations of 25-hydroxyvitamin D shows recent modest increases”
Authors: R.L. Schleicher et al.